PROJECT SUMMARY Adhesive receptors are a class of cell surface receptor that binds to surface-bound ligands to mediate cell adhesion to other cells or tissues. Adhesive receptors play a critical role in physiology and disease, and so are common targets for therapeutic interventions for a wide range of diseases. The goal of this project is to understand the dynamic conformational changes that allow adhesive receptors to mediate strong cell adhesion in vivo, in order to develop better methods for their inhibition. This project focuses on the bacterial adhesin FimH, which is implicated in infection of the urinary tract by Escherichia coli. This should provide alternative methods to treat or prevent infections involving antibiotic-resistant bacteria. The novelty of this project is that it addresses how mechanical force regulates the dynamic conformational changes of adhesive receptors. This project tests the hypothesis that FimH utilizes tensile mechanical force transmitted by the bound ligand to close the binding pocket tightly around the ligand, allowing extremely tight binding in the presence of mechanical force. This project will test the hypothesis that a novel type of 'parasteric' inhibitor can directly open the FimH binding pocket even in the presence of mechanical force. The project will also test the hypothesis that FimH will be more effectively inhibited in physiological conditions by parasteric inhibitors than by conventional orthosteric or allosteric inhibitors. The following approaches will be used to obtain these goals. 1) The binding kinetics of FimH will be measured, both with and without mechanical force, in the presence of parasteric, orthosteric and allosteric inhibitory antibodies. 2) The structure and conformational dynamics of FimH will be determined in the presence of three types of antibodies using NMR, X-ray crystallography and atomistic structural simulations. 3) The effectiveness of the three types of antibodies will be compared, for preventing bacterial adhesion to uroepithelial cells, as well a urinary tract infections in mice. This work will provide rationale for FimH vaccine and inhibitor designs. This work will also provide rationale for developing inhibitors for many other adhesive receptors, which are attractive targets for therapeutic interventions for thrombotic and inflammatory diseases, cancer, and many other diseases.